Alternate approach to updating paint property nodes

third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.cpp

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/paint/PaintPropertyTreeBuilder.h"
 
 #include "core/frame/FrameView.h"
 #include "core/frame/LocalFrame.h"
 #include "core/frame/Settings.h"
 #include "core/layout/LayoutInline.h"
@@ skipping 88 matching lines @@
 static FloatPoint3D transformOrigin(const LayoutBox& box)
 {
     const ComputedStyle& style = box.styleRef();
     FloatSize borderBoxSize(box.size());
     return FloatPoint3D(
         floatValueForLength(style.transformOriginX(), borderBoxSize.width()),
         floatValueForLength(style.transformOriginY(), borderBoxSize.height()),
         style.transformOriginZ());
 }
 
+void PaintPropertyTreeBuilder::clearTransformProperty(const LayoutObject& object, void (ObjectPaintProperties::*setter)(PassRefPtr<TransformPaintPropertyNode>))
+{
+    if (ObjectPaintProperties* existingProperties = object.objectPaintProperties())
+        (existingProperties->*setter)(nullptr);
+}
+
+void PaintPropertyTreeBuilder::updateOrCreateTransformProperty(const LayoutObject& object, TransformPaintPropertyNode* (ObjectPaintProperties::*getter)() const, void (ObjectPaintProperties::*setter)(PassRefPtr<TransformPaintPropertyNode>), const TransformationMatrix& matrix, const FloatPoint3D& origin, PassRefPtr<TransformPaintPropertyNode> parent)
+{
+    ObjectPaintProperties* existingProperties = object.objectPaintProperties();
+    TransformPaintPropertyNode* existingTransform = existingProperties ? (existingProperties->*getter)() : nullptr;
+    if (!existingTransform) {

[pdr., 2016/07/21 23:14:01]

Oops, you'll want to do a comparison of the values here too. Something like:
if (!existingTransform || existingTransform->matrix() != matrix ||
existingTransform->origin() != origin)

+        (object.getMutableForPainting().ensureObjectPaintProperties().*setter)(TransformPaintPropertyNode::create(matrix, origin, parent));
+        return;
+    }
+    existingTransform->setMatrix(matrix);
+    existingTransform->setOrigin(origin);
+    existingTransform->setParent(parent);
+}
+
 void PaintPropertyTreeBuilder::updateTransform(const LayoutObject& object, PaintPropertyTreeBuilderContext& context)
 {
     if (object.isSVG() && !object.isSVGRoot()) {
         // SVG does not use paint offset internally.
         DCHECK(context.current.paintOffset == LayoutPoint());
 
         // FIXME(pdr): Check for the presence of a transform instead of the value. Checking for an
         // identity matrix will cause the property tree structure to change during animations if
         // the animation passes through the identity matrix.
         // FIXME(pdr): Refactor this so all non-root SVG objects use the same transform function.
         const AffineTransform& transform = object.isSVGForeignObject() ? object.localSVGTransform() : object.localToSVGParentTransform();
-        if (transform.isIdentity())
+        if (transform.isIdentity()) {
+            clearTransformProperty(object, &ObjectPaintProperties::setTransform);
             return;
+        }
 
         // The origin is included in the local transform, so use an empty origin.
-        RefPtr<TransformPaintPropertyNode> svgTransform = TransformPaintPropertyNode::create(
-            transform, FloatPoint3D(0, 0, 0), context.current.transform);
-        context.current.transform = svgTransform.get();
-        object.getMutableForPainting().ensureObjectPaintProperties().setTransform(svgTransform.release());
+        updateOrCreateTransformProperty(object, &ObjectPaintProperties::transform, &ObjectPaintProperties::setTransform, transform, FloatPoint3D(0, 0, 0), context.current.transform);
+        context.current.transform = object.objectPaintProperties()->transform();
         return;
     }
 
     const ComputedStyle& style = object.styleRef();
-    if (!object.isBox() || !style.hasTransform())
+    if (!object.isBox() || !style.hasTransform()) {
+        clearTransformProperty(object, &ObjectPaintProperties::setTransform);
         return;
+    }
 
     TransformationMatrix matrix;
     style.applyTransform(matrix, toLayoutBox(object).size(), ComputedStyle::ExcludeTransformOrigin,
         ComputedStyle::IncludeMotionPath, ComputedStyle::IncludeIndependentTransformProperties);
-    RefPtr<TransformPaintPropertyNode> transformNode = TransformPaintPropertyNode::create(
-        matrix, transformOrigin(toLayoutBox(object)), context.current.transform);
-    context.current.transform = transformNode.get();
-    object.getMutableForPainting().ensureObjectPaintProperties().setTransform(transformNode.release());
+    updateOrCreateTransformProperty(object, &ObjectPaintProperties::transform, &ObjectPaintProperties::setTransform, matrix, transformOrigin(toLayoutBox(object)), context.current.transform);
+    context.current.transform = object.objectPaintProperties()->transform();
 }
 
 void PaintPropertyTreeBuilder::updateEffect(const LayoutObject& object, PaintPropertyTreeBuilderContext& context)
 {
     if (!object.styleRef().hasOpacity())
         return;
     RefPtr<EffectPaintPropertyNode> effectNode = EffectPaintPropertyNode::create(object.styleRef().opacity(), context.currentEffect);
     context.currentEffect = effectNode.get();
     object.getMutableForPainting().ensureObjectPaintProperties().setEffect(effectNode.release());
 }
@@ skipping 226 matching lines @@
         if (boxModelObject.isTableCell()) {
             LayoutObject* parentRow = boxModelObject.parent();
             ASSERT(parentRow && parentRow->isTableRow());
             context.current.paintOffset.moveBy(-toLayoutBox(parentRow)->topLeftLocation());
         }
     }
 }
 
 void PaintPropertyTreeBuilder::buildTreeNodes(const LayoutObject& object, PaintPropertyTreeBuilderContext& context)
 {
-    object.getMutableForPainting().clearObjectPaintProperties();
-
     if (!object.isBoxModelObject() && !object.isSVG())
         return;
 
     deriveBorderBoxFromContainerContext(object, context);
 
     updatePaintOffsetTranslation(object, context);
     updateTransform(object, context);
     updateEffect(object, context);
     updateCssClip(object, context);
     updateLocalBorderBoxContext(object, context);
     updateScrollbarPaintOffset(object, context);
     updateOverflowClip(object, context);
     // TODO(trchen): Insert flattening transform here, as specified by
     // http://www.w3.org/TR/css3-transforms/#transform-style-property
     updatePerspective(object, context);
     updateSvgLocalToBorderBoxTransform(object, context);
     updateScrollTranslation(object, context);
     updateOutOfFlowContext(object, context);
 }
 
 } // namespace blink